CN102203546A - Device for measuring a fluid meniscus - Google Patents

Abstract

The invention relates to a device (102) arranged for measuring a geometry of a fluid meniscus (132). The device comprises a fluid chamber (104) storing a first electrically conductive fluid (128) and a second electrically insulating fluid (324). The fluids are mutually immiscible and define a fluid meniscus (132) in between them. Furthermore a main electrowetting electrode (118) and auxiliary electrowetting electrodes (120, 122, 124, 126) are provided for controlling the geometry of the fluid meniscus. Hereto a voltage source (134) for providing a voltage between the main electrowetting electrode and the auxiliary electrowetting electrodes is comprised, as well as a measurement circuit (144) for separately measuring capacitances between the main electrowetting electrode and at least two of the auxiliary electrowetting electrodes. For this purpose the measurement circuit comprises a multiplexer for demodulating a signal indicative for said capacitances. The invention further relates to a method for measuring a fluid meniscus.

Description

Devices for measuring fluid menisci

technical field

The invention relates to a device for measuring the geometry of a fluid meniscus.

The invention also relates to a catheter comprising such a device.

The invention also relates to a method for measuring the geometry of a fluid.

Background technique

A controllable optical lens system is disclosed in WO2006/035407A1. The system includes a lens having a cavity containing first and second fluids, wherein an interface between the fluids defines a lens surface. The system also includes: an electrode arrangement comprising a first electrode and a second electrode for electrically controlling the shape of the lens surface; a feedback control loop for controlling the electrode arrangement based on a signal provided by a capacitance sensing device for use with for measuring the capacitance between the first and second electrodes.

The technique disclosed in WO2006/035407A1 is not well suited for generating specific geometries of fluid menisci, such as a sloped flat meniscus or a symmetrical concave or convex shape.

Contents of the invention

It is an object of the present invention to provide a device as described in the introduction for more precise measurement of the geometry of a fluid meniscus. This object is achieved by a device according to the invention comprising: a fluid chamber comprising a first fluid and a second fluid, said first fluid being electrically conductive, said second fluid being electrically insulating, and said The first and second fluids are mutually immiscible and contact each other on the fluid meniscus; the primary electrowetting electrode and the auxiliary electrowetting electrode are used to control the geometry of the fluid meniscus, the primary electrowetting electrode a wetting electrode located in the main plane, the auxiliary electrowetting electrode partially surrounding the fluid chamber and located in the auxiliary plane; a voltage source for providing the main electrowetting electrode and a plurality of auxiliary electrowetting electrodes voltage between; a measurement circuit for measuring the capacitance between the main electrowetting electrode and at least two auxiliary electrowetting electrodes respectively, said measurement circuit comprising a multiplexer for demodulating a signal indicative of said capacitance With device.

By providing a plurality of auxiliary electrowetting electrodes, and by measuring the capacitance between said main electrowetting electrode and at least two of said auxiliary electrowetting electrodes, the geometry of the fluid meniscus advantageously allows a more accurate . The auxiliary electrowetting electrodes are electrically connected to each other via a conductive first fluid contained in the fluid cavity. Thus, depending on the properties of the first fluid, there is a significant interaction between the auxiliary electrowetting electrodes. Interactions between auxiliary electrodes prevent determination of individual capacitances. That is, the signal representing the capacitance between the main electrowetting electrode and the auxiliary electrowetting electrode is indicative of the bulk properties due to the interaction. In order to counteract the consequences of the interaction between the auxiliary electrowetting electrodes, the device according to the invention provides a multiplexer for demodulating the signal representing the capacitance between the main electrowetting electrode and each auxiliary electrowetting electrode . More specifically, the signal is decomposed into components representing the capacitance associated with individual auxiliary electrowetting electrodes. Therefore, the capacitance between the main electrowetting electrode and at least two auxiliary electrowetting electrodes is amenable for) were measured separately. That is, more information about the actual geometry of the fluid meniscus is available. As a result, the device according to the invention enables a more precise measurement of the geometry of the fluid meniscus.

In a preferred embodiment of the device according to the invention, said measuring circuit is arranged for measuring the capacitance between said main electrowetting electrode and each of said auxiliary electrowetting electrodes. This has the advantage that more information about the geometry of the fluid meniscus will become available.

In a preferred embodiment of the device according to the invention, the device comprises a voltage control circuit for controlling the voltage across said main electrowetting electrode and each of said auxiliary electrowetting electrodes based on a control signal provided by said measurement circuit. voltage provided between. The benefit of this feature is to compensate for deviations between the actual geometry of the fluid meniscus and the desired geometry of the fluid meniscus. Said deviations may be due to possible manufacturing tolerances, or in situ modification of the fluid contained in the fluid cavity due to, for example, temperature variations. Also, where the density of the first fluid differs from the density of the second fluid, deviations result from changes in the orientation of the fluid cavity relative to the gravitational field. Compensation for the aforementioned deviation is accomplished by the voltage control circuit by comparing the signal provided by the measurement circuit with a set point signal representing the desired geometry of the fluid meniscus; A possible difference between the supplied signal and the set point signal, provides the appropriate voltage between the primary electrowetting electrode and each auxiliary electrowetting electrode.

In another preferred embodiment of the device according to the invention, said measuring circuit comprises an operational amplifier for measuring the capacitance between said main electrowetting electrode and at least two of said auxiliary electrowetting electrodes. The operational amplifier is configured with a negative feedback loop configured with a predetermined measurement capacitance, wherein the operational amplifier is arranged to cooperate with an input of the multiplexer. An advantage of the measuring circuit of the embodiments in question is that it is able to counteract disturbing effects due to possible parasitic capacitances which prevent the measurement of the capacitance between the main electrowetting electrode and each auxiliary electrowetting electrode. Measure precisely.

A potential source of this parasitic capacitance is the coaxial measurement cable. Concerned embodiments of the device according to the invention may thus be particularly beneficial for applications in which the arrangement of fluid chamber, primary electrowetting electrode and auxiliary electrowetting electrode is located remotely from the measurement circuit. Here, the device and the measurement circuit are preferably interconnected via a coaxial cable. An example of such an application is given by a catheter, where the device is mounted within the tip of the catheter for redirecting ultrasound and/or laser beams during scanning. In view of the relatively small size of the tip of the catheter, the measuring circuit cannot be integrated in the tip of the catheter. Another advantage of this embodiment therefore lies in the fact that it enables the use of the device in catheters.

In this particular example, each auxiliary electrowetting electrode is associated with at least one parasitic capacitance. In addition to this, parasitic capacitances are interconnected. That is, the capacitance between the main electrowetting electrode and the auxiliary electrowetting electrode interacts via the first and second fluid contained in the fluid cavity. In addition to this, the parasitic capacitance is not constant due to the bending motion of the coaxial cable during use.

In a further embodiment of the device according to the invention, the measurement circuit comprises a switching circuit comprising a first measurement capacitor with a predetermined first measurement capacitance and a second measurement capacitor with a predetermined second measurement capacitance, wherein the first and the second measurement capacitor being different from each other, the switch circuit further comprising switches for driving the first and second measurement capacitors in an alternating and mutually exclusive manner, wherein the switch circuit is arranged for use with the multiplex The inputs of the multiplexer cooperate. An advantage of the measurement circuit of the embodiments involved is that it is able to eliminate disturbing effects due to possible parasitic capacitances which prevent accurate measurement of the capacitance between the main and auxiliary electrowetting electrodes .

In a preferred embodiment of the device according to the invention, said multiplexer is a frequency domain multiplexer and said voltage source is arranged for providing a voltage at a specific frequency. The frequency domain multiplexer demodulates a signal representing the capacitance between the primary electrowetting electrode and the auxiliary electrowetting electrode by employing a demodulation signal, each demodulated signal having a voltage source corresponding to the corresponding auxiliary electrowetting electrode. The frequency components corresponding to the frequency of the drive.

In a practical embodiment of the device according to the invention, said multiplexer is a time domain multiplexer. The time domain multiplexer demodulates a signal representing the capacitance between the primary electrowetting electrode and the secondary electrowetting electrode by employing a demodulation signal, wherein each demodulation signal is a signal having a low value and a high value square wave signal. The voltage source includes a voltage switch for alternately disconnecting the voltage corresponding to the high value of the respective demodulation value. In case the square wave signal reaches its low value, the corresponding voltage is disconnected by the corresponding voltage switch. When the square wave signal reaches its high value, the corresponding voltage is connected through the accompanying voltage switch.

In another practical embodiment of the device according to the invention, said first fluid provides a first speed of sound and said second fluid provides a second speed of sound, wherein the first and second speed of sound are different from each other. That is, the speed of sound through the first fluid has a first value and the speed of sound through the second fluid has a second value, wherein the first and second values are different from each other. As a result, by properly controlling the geometry of the fluid meniscus, the fluid meniscus is able to redirect sound. A possible application of the embodiments involved is controlling the direction of an ultrasound beam.

In another practical embodiment of the device according to the invention, said first fluid has a first refractive index and said second fluid has a second refractive index, wherein the first and second refractive indices are different. As a result, by properly controlling the geometry of the fluid meniscus, the fluid meniscus can redirect electromagnetic radiation, such as a laser beam.

Another object of the present invention is to provide a method for measuring the geometry of a fluid meniscus between an electrically conductive first fluid and an electrically insulating second fluid contained in a fluid cavity, the fluids not mixing with each other The method comprises the steps of: providing a voltage between a main electrowetting electrode located in a main plane and an auxiliary electrowetting electrode partially surrounding the a fluid cavity and located in the auxiliary plane; and measuring the capacitance between the main electrowetting electrode and at least two auxiliary electrowetting electrodes respectively by means of a measurement circuit comprising a multiplexer.

In a preferred embodiment of the method according to the invention there is provided a step for controlling a voltage applied to said auxiliary electrowetting electrode, wherein said voltage is based on a signal provided by said measurement circuit.

Another object of the present invention is to provide a catheter for real-time control of the direction of sound and/or electromagnetic radiation. This object of the invention is achieved by a catheter according to the invention provided with a device according to the invention.

The invention also relates to the use of the device according to the invention as defined in claims 11 to 13 in catheters, optical storage devices and optical cameras.

Description of drawings

Figure 1A schematically depicts a device comprising a fluid chamber, a primary electrowetting electrode and an auxiliary electrowetting electrode in a cross-sectional view.

Figure IB schematically shows a bottom view of the device depicted in Figure IA.

Figure 2 schematically shows a model of the electrical characteristics of an electrowetting lens together with a coaxial cable and a measurement circuit applied to the device according to Figures 1A and 1B.

Figure 3A schematically depicts in cross-sectional view a device comprising a fluid chamber, a primary electrowetting electrode and an auxiliary electrowetting electrode, the device also comprising a measurement circuit configured with a time domain multiplexer.

Figure 3B schematically shows a bottom view of the device depicted in Figure 3A.

Figure 4 schematically shows a model of the electrical characteristics of an electrowetting lens together with a coaxial cable and a measurement circuit applied to the device of Figures 3A and 3B.

Figure 5 depicts a flowchart representative of a method for measuring the geometry of a fluid meniscus.

Detailed ways

A first embodiment of the device according to the invention is depicted in FIGS. 1A , 1B and 2 . Figure 1A depicts a cross-sectional and bottom view of device 102, while Figure IB shows a bottom view of the device. The device 102 includes a fluid chamber 104 having a bottom 106 and walls including wall portions 108, 110, 112 and 114, see also FIG. 1B. The wall portions 108, 110, 112 and 114 are provided with an insulating layer 116 for preventing short circuits, see FIG. 1A. In alternative embodiments, the fluid cavity may have conical or cylindrical walls, or any other suitable walls. Apparatus 102 also includes: primary electrowetting electrode 118, which in this particular embodiment is attached to base 106; and auxiliary electrowetting electrodes 120, 122, 124, and 126, see FIG. The auxiliary electrowetting electrodes partially surround the fluid chamber 104 and are attached to the walls 108, 110, 112 and 114, respectively. In this particular example, primary plane 119 and secondary planes 121, 123, 125, and 127 do not coincide.

Referring to FIG. 1A , fluid cavity 104 includes a first fluid 128 and a second fluid 130 that are mutually immiscible and define a fluid meniscus 132 as the interface between fluids 128 and 130 . The first fluid 128 is electrically conductive and the second fluid 130 is electrically insulating. That is, the first fluid 128 has a first electrical conductivity and the second fluid 130 has a second electrical conductivity, wherein the second electrical conductivity is comparatively significantly less than the first electrical conductivity. Ideally, the second conductivity is zero (nihil). Preferably, the density of the first fluid and the density of the second fluid do not significantly differ from each other, making the device 102 less sensitive to changes in its orientation relative to the gravitational field.

₁和 ₂来控制流体弯月面132的几何形状，见图1A。接触角

₁限定为流体弯月面132和壁部108之间的角度，接触角

₂相应地限定为流体弯月面132和壁部112之间的角度，见图1B。在此实施例中，目的是生成倾斜的直流体弯月面，如图1A所示。通过采用电润湿效应来控制接触角。通过测量主电润湿电极116和每个辅助电润湿电极120、122、124和126之间的电容来估算接触角。也就是说，前述电容由覆盖有导电的第一流体128的电润湿电极的区域136和138的尺寸确定，其中覆盖有导电的第一流体128的区域136和138与所述接触角成比例地变化。流体弯月面132和壁部110以及114之间的接触角同等地被控制。 During operation, voltages V ₁ , V ₂ , V ₃ and V ₄ are supplied by voltage source 134 to corresponding auxiliary electrowetting electrodes 120 , 122 , 124 and 126 at frequencies f ₁ , f ₂ , f ₃ and f ₄ , respectively. . Here, f ₁ ≠f ₂ ≠f ₃ ≠f ₄ holds true. By providing the voltage to the auxiliary electrowetting electrodes 120, 122, 124 and 126, via controlling the contact angle

₁ and ₂ to control the geometry of the fluid meniscus 132, see FIG. 1A. Contact angle

₁ is defined as the angle between the fluid meniscus 132 and the wall 108, the contact angle

₂ is correspondingly defined as the angle between the fluid meniscus 132 and the wall portion 112, see FIG. 1B . In this example, the aim is to generate an inclined straight fluid meniscus, as shown in Figure 1A. The contact angle is controlled by exploiting the electrowetting effect. The contact angle was estimated by measuring the capacitance between the main electrowetting electrode 116 and each auxiliary electrowetting electrode 120 , 122 , 124 and 126 . That is, the aforementioned capacitance is determined by the dimensions of the regions 136 and 138 of the electrowetting electrode covered with the conductive first fluid 128, wherein the regions 136 and 138 covered with the conductive first fluid 128 are proportional to the contact angle change. The contact angles between fluid meniscus 132 and walls 110 and 114 are equally controlled.

In this particular example, the device 102 is mounted within the distal end 140 of the catheter for the purpose of real-time control of the direction of an ultrasound beam 142 generated by an ultrasound transducer 144, as depicted in FIG. 1A. For this purpose, the first fluid provides a first speed of sound and the second fluid provides a second speed of sound, wherein the first speed of sound is different from the second speed of sound. The discontinuity in sound velocity that occurs at the fluid meniscus 132 will redirect the ultrasound beam. Thus, by controlling the inclination of the fluid meniscus, the ultrasound beam 142 is steered to a target location, eg, inside the human body. The reader is referred to WO2006/035407A1 for more detailed information. Device 102 is not limited to application in catheters; other promising applications are endoscopes, biopsy needles, and scanning microscopes.

Due to the relatively small size of the catheter tip, measurement circuit 144 and voltage source 134 cannot be integrated with catheter tip 140 . Accordingly, measurement circuit 144 and voltage source 134 are located remotely from tip 140 of the catheter. The measurement circuit 144 is arranged for measuring the capacitance between the main electrowetting electrode 118 and the auxiliary electrowetting electrodes 120 , 122 , 124 and 126 , respectively, based on the signal 153 . Signal 153 is indicative of the capacitance between primary electrowetting electrode 118 and each of auxiliary electrowetting electrodes 120, 122, 124, and 126, denoted by _C1 , _C2 , _C3 , and _C4 , respectively, see FIG. 1A and Figure 1B. Thus in this particular example, each of the auxiliary electrowetting electrodes 120 , 122 , 124 and 126 is taken into account by the measurement circuit 144 . Measurement circuit 144 and voltage source 134 are physically connected to electrowetting lens 102 by coaxial cables 146 , 148 , 150 , 151 , and 152 . Although the coaxial cables are shielded so that there is no mutual coupling between the coaxial cables, the coaxial cables 146, 148, 150, 151 and 152 introduce significant parasitic capacitors with parasitic capacitances C _P1 , C _P2 , C _P3 , C _P4 and C _P5 . Due to the bending motion of the coaxial cables 146, 148, 150, 151 and 152 during use, the parasitic capacitance is not constant. Note that the cables 146, 148, 150 and 151 may be implemented by common electrically insulated cables, between which cable parasitic capacitances will develop.

FIG. 2 illustrates a model of the electrical characteristics of device 102 . Furthermore, FIG. 2 depicts in more detail the measurement circuit 144 employed in the apparatus of FIGS. 1A and 1B . For the purpose of measuring capacitances C ₁ , C ₂ , C ₃ and C ₄ respectively, measurement circuit 202 includes an operational amplifier 204 configured with a negative feedback loop 206 configured with a measurement capacitor 208 having a measurement capacitance C _meas . The positive input of the op amp, V _+, is grounded. Due to the negative feedback loop 206, the negative input terminal V ₋ of the operational amplifier 204 is at virtual ground, that is, V ₋ =V ₊ holds true. The latter means V _- =0[V]. Although current will flow through the parasitic capacitances C _{P1 ,} C _P2 , C _P3 , C _P4 , the voltages across capacitors C ₁ , C ₂ , C _{3 ,} and C ₄ are equal to V ₁ , V ₂ , V ₃ , and V ₄ , respectively. Current flowing through C ₁ , C ₂ , C _{3 ,} and C ₄ will not flow through C _p5 because this capacitor is connected to the op amp's negative input, V ₋ , which is at virtual ground. The voltage V _meas characterizing the signal 210 representing the capacitance between the primary electrowetting electrode 118 and the auxiliary electrowetting electrodes 120, 122, 124, and 126 is thus derived from the following equation:

[1],

where ω corresponds to the imaginary part of the Laplace variable and j denotes the imaginary unit. Furthermore, V _meas is the voltage measured across the capacitance C _meas using a voltmeter known per se.

The measurement circuit 202 also includes a multiplexer 212, which employs frequency domain multiplexing in this particular example. Alternatively, time domain multiplexing can be utilized. An operational amplifier 204 cooperates with an input 211 of a multiplexer 212 . Multiplexer 212 replicates signal 210 representing capacitances C ₁ , C ₂ , C _{3 ,} and C ₄ into a plurality of signals 214 , 216 , 218 , and 220 representing the capacitances, respectively. The number of replicates corresponds to the number of auxiliary electrowetting electrodes. After replication, the signals 214, 216, 218 and 220 are demodulated with demodulated signals having frequencies fi _{, f2} , _f3 and _f4, respectively. The frequency of the demodulated signal is equal to the frequency at which the auxiliary electrowetting electrodes 120 , 122 , 124 and 126 (see FIG. 1B ) are driven by the voltage source 134 . The demodulated signal may be sinusoidal. Alternatively, the demodulated signal may be embodied by a square wave or any other suitable waveform. The frequencies f ₁ , f ₂ , f ₃ and f ₄ are such that after demodulation only one frequency component of the signals 214 , 216 , 218 and 220 (see FIG. 2 ) is demodulated to DC, ie 0 [Hz], while Possible other frequency components present in the demodulated signals 222, 224, 226 and 228 are sufficiently far from 0 [Hz], eg at least 100 [Hz].

During operation, the demodulated signals 222, 224, 226, and 228 are filtered through low-pass filters 230, 232, 234, and 236, respectively, with cutoff frequencies such that the DC of the demodulated signals Components are left unaffected while higher frequency components are effectively attenuated. The low-pass filtered signals 238, 240, 242, and 244 are characterized by voltages V _meas,1 , V _meas,2 , V _meas,3 , and V _meas,4 which are related to capacitances C ₁ , C _2. C ₃ and C ₄ are related:

[2]，

[2],

in . Accordingly, each capacitance _Ck between the primary electrowetting electrode 118 and the auxiliary electrowetting electrodes 120, 122, 124, and 126 may be determined according to the following relationship:

[3]，

[3],

。应强调，依照本发明的第一实施例不必局限于数目为4的辅助电润湿电极，即系数k允许取任何正整数，只要所述整数不小于2。 in

. It should be emphasized that the first embodiment according to the invention is not necessarily limited to a number of 4 auxiliary electrowetting electrodes, ie the coefficient k is allowed to take any positive integer as long as said integer is not less than 2.

表示。在此具体实施例中，

为四维向量，其包括流体弯月面132分别和壁部108、110、112和114之间的每个接触角

₁、

₂、

₃（未示出）和

₄（未示出）的参考。接触角设定点

通过转换表158的方式转换为电容设定点。电容设定点

为电容C₁、C₂、C₃和C₄的四维参考向量，即主电润湿电极和辅助电润湿电极120、122、124和126之间的电容。转换表158可以例如通过实验获得。在四维求和点160，电容设定点

与测量电容

比较，其中

为包括由测量电路144确定的电容C₁、C₂、C₃和C₄的向量。响应于

和

之间的差异∆，即，控制器162提供四维电压控制信号164到电压源134。电压控制信号164也被提供到测量电路144，从而使得所述测量电路能够依照方程[3]进行计算。接着，电压源134分别提供前述电压V₁、V₂、V₃和V₄到辅助电润湿电极120、122、124和126。注意，纯粹是出于此特定实施例的目的，电压控制电路154专用于控制数目为4个的电压。也就是说，前述电压控制电路控制的电压的数目不受限制，只要所述数目至少为2。 Referring to FIGS. 1A and 1B , voltage control circuit 154 is depicted. The voltage control circuit 154 is arranged for the purpose of controlling the voltages V ₁ , V ₂ , V ₃ and V ₄ , such that the actual geometry of the fluid meniscus 132 coincides with the desired geometry of the fluid meniscus 132 . For the geometry of the fluid meniscus 132, the desired geometry is determined by the contact angle set point

express. In this specific example,

is a four-dimensional vector that includes each contact angle between fluid meniscus 132 and walls 108, 110, 112, and 114, respectively

₁ .

₂ .

₃ (not shown) and

₄ (not shown) reference. contact angle set point

Convert to capacitive set point by means of conversion table 158 . Capacitance set point

is the four-dimensional reference vector of the capacitances C ₁ , C ₂ , C ₃ and C ₄ , that is, the capacitances between the main electrowetting electrode and the auxiliary electrowetting electrodes 120 , 122 , 124 and 126 . The conversion table 158 can be obtained, for example, through experiments. At point 160 of the four-dimensional summation, the capacitive set point

with measuring capacitance

compare, where

is a vector including the capacitances C ₁ , C ₂ , C ₃ , and C ₄ determined by the measurement circuit 144 . in response to

and

The difference ∆ between , the controller 162 provides a four-dimensional voltage control signal 164 to the voltage source 134 . A voltage control signal 164 is also provided to the measurement circuit 144, enabling said measurement circuit to perform calculations according to equation [3]. Next, the voltage source 134 provides the aforementioned voltages V ₁ , V ₂ , V ₃ and V ₄ to the auxiliary electrowetting electrodes 120 , 122 , 124 and 126 , respectively. Note that voltage control circuit 154 is dedicated to controlling a number of four voltages purely for the purposes of this particular embodiment. That is, the number of voltages controlled by the aforementioned voltage control circuit is not limited as long as the number is at least two.

A second embodiment of the invention is depicted in FIGS. 3A , 3B and 4 . FIG. 3A depicts a cross-sectional view of an apparatus 302 and FIG. 3B shows a bottom view of the apparatus 302 . The device 302 includes a fluid chamber 304 having a top 306 and a wall having wall portions 308, 310, 312 and 314, see Fig. 3B. The wall portions 308, 310, 312 and 314 are provided with an insulating layer 316 for preventing short circuits, see Fig. 3A. In alternative embodiments, fluid cavity 304 may have conical or cylindrical walls, or any other suitable walls. Device 302 includes a grounded primary electrowetting electrode 318 attached to top 306 . In this particular example, device 302 includes two auxiliary electrowetting electrodes 320 and 322 that partially surround fluid cavity 304 and are attached to walls 308 and 312, respectively.

As shown in FIG. 3A , the fluid cavity 304 includes a first fluid 324 and a second fluid 326 that are mutually immiscible and contact each other at a fluid meniscus 328 . The first fluid 324 is electrically conductive and the second fluid 326 is electrically insulating. That is, the first fluid 324 has a first electrical conductivity and the second fluid 326 has a second electrical conductivity, wherein the second electrical conductivity is significantly less than the first electrical conductivity by comparison. Ideally, the second conductivity is zero.

₂控制流体弯月面328的几何形状。接触角

₁限定为流体弯月面328和壁部308之间的角度，接触角

₂因此限定为流体弯月面328和壁部312之间的角度。此实例中目的是生成流体弯月面328的面向上的几何形状，也就是说，从流体腔体304底部看到的几何形状。通过采用电润湿效应控制所述接触角。通过测量主电润湿电极318和每个辅助电润湿电极320和322之间的电容来估算接触角

₁和

₂。也就是说，前述电容由电润湿电极的覆盖有导电的第一流体324的区域332和334的尺寸确定，其中覆盖有导电的第一流体324的区域332和334随着接触角

₁和

₂成比例地变化。电压V₁和V₂分别通过第一电压开关331和第二电压开关333而交替地断开。在时间段t₁期间，电压V₁被连接而电压V₂被断开。在时间段t₂期间，电压V₂被连接而电压V₁不连接。因此，每次驱动辅助电润湿电极320和322之一，即时间段t₁和t₂连续重复。 During use, voltages V ₁ and V ₂ are applied by voltage source 330 to auxiliary electrowetting electrodes 320 and 322 . By providing the voltage to the auxiliary electrowetting electrodes 320 and 322, via controlling the contact angle ₁ and

₂ Controlling the geometry of the fluid meniscus 328. Contact angle

₁ is defined as the angle between the fluid meniscus 328 and the wall 308, the contact angle

₂ is thus defined as the angle between the fluid meniscus 328 and the wall portion 312. The goal in this example is to generate the upward facing geometry of the fluid meniscus 328 , that is, the geometry seen from the bottom of the fluid cavity 304 . The contact angle is controlled by exploiting the electrowetting effect. The contact angle was estimated by measuring the capacitance between the primary electrowetting electrode 318 and each of the auxiliary electrowetting electrodes 320 and 322

₁ and

₂ . That is, the aforementioned capacitance is determined by the size of the regions 332 and 334 of the electrowetting electrode covered with the conductive first fluid 324, wherein the regions 332 and 334 covered with the conductive first fluid 324 increase with the contact angle

₁ and

₂ varies proportionally. The voltages _V1 and _V2 are alternately disconnected by the first voltage switch 331 and the second voltage switch 333, respectively. During time period _t1 , voltage _V1 is connected and voltage _V2 is disconnected. During time period _t2 , voltage _V2 is connected and voltage _V1 is not connected. Thus, each time one of the auxiliary electrowetting electrodes 320 and 322 is driven, the time periods _t1 and _t2 repeat continuously.

₂，将激光束338聚焦到例如光学存储盘上的目标位置。 In this embodiment, device 302 is mounted in an optical storage drive for the purpose of real-time control of the direction of laser beam 338 generated by laser 340, see Figure 3A. For this purpose, the first fluid 324 has a first refractive index and the second fluid 326 has a second refractive index, wherein the first and second refractive indices are different from each other. The discontinuity in refractive index that occurs at fluid meniscus 328 redirects laser beam 338 provided by laser 340 . Therefore, by controlling the contact angle ₁ and

_2. Focus the laser beam 338 onto, for example, a target location on an optical storage disc.

Measurement circuitry 342 and voltage source 330 are located remotely from electrowetting lens 302, as depicted in Figures 3A and 3B. The measurement circuit 342 is arranged for measuring the capacitance between the main electrowetting electrode 318 and the auxiliary electrowetting electrodes 320 and 322, denoted by _C1 and _C2 , respectively. Measurement circuit 342 and voltage source 330 are preferably physically connected to device 302 by coaxial cables 344 , 346 and 348 . Although the coaxial cables 344, 346 and 348 are shielded so that no mutual coupling is formed between the coaxial cables, the coaxial cables introduce significant parasitic capacitors having capacitances C _P1 , C _P2 and C _P3 . The parasitic capacitance is not constant due to the bending motion of the coaxial cables 344, 346 and 348 during use.

。开关电路404还包括电容开关410，其用于以交替且相互排斥的方式驱动第一和第二测量电容器406和408。通过第一电压开关407和第二电压开关409，电压V₁和V₂分别被交替地断开。 FIG. 4 depicts a model of the electrical characteristics of device 302 . Furthermore, Figure 4 depicts in more detail the measurement circuit 342 employed in the device of Figures 3A and 3B. For the purpose of measuring capacitances C ₁ and C ₂ respectively, measurement circuit 402 includes switching circuit 404 . The switching circuit 404 includes a first measurement capacitor 406 having a known capacitance C _meas and a first measurement capacitor 406 having a known capacitance The second measurement capacitor 408, where

. The switching circuit 404 also includes a capacitive switch 410 for driving the first and second measurement capacitors 406 and 408 in an alternating and mutually exclusive manner. Via the first voltage switch 407 and the second voltage switch 409, the voltages V ₁ and V ₂ are alternately switched off, respectively.

由下述方程给出，所述电压表征在时间段t₁的第一部分期间的信号412，所述信号412代表电容C₁和C₂： The situation during time period _t1 is that _V2 is not connected. During a first portion of time period t ₁ , capacitive switch 410 enables first measurement capacitor 406 and during a second portion of time period t ₁ capacitive switch 410 enables second measurement capacitor 408 . Therefore during the first part of time period _t1 , the voltage

The voltage characterizes the signal 412 during the first part of the time period t ₁ , the signal 412 representing the capacitances C ₁ and C ₂ , given by the following equation:

[4]，

[4],

where C _R2 represents the resulting capacitance due to C _P2 and C ₂ , which is defined according to the following equation:

[5]。

[5].

的下述表述，所述电压表征在时间段t₁的第二部分期间的信号412： Similarly, for the case where the second measurement capacitor 408 is enabled, the voltage

The following representation of the voltage characterizing the signal 412 during the second part of the time period _t1 :

[6]。

[6].

Considering equations [4] and [6], it is assumed that the resulting capacity C _R2 remains constant during the time period t ₁ . The time period t ₁ is associated with a sample frequency of typically 1 kHz to 1 MHz, which is a frequency significantly greater than the bandwidth of the first and second fluids 324 and 326 contained in the fluid cavity 304 . Therefore, the latter assumption is reasonable and therefore does not degrade the accuracy associated with the measurement of capacitances C ₁ and C ₂ . Combining equations [4] and [6] yields a system of two linear equations. The latter system contains two unknowns, capacitance C ₁ and parasitic capacitance C _p3 . The system of linear equations can be solved to obtain the unknown capacitance C ₁ , the solution is given by the following equation:

[7]。

[7].

由下述方程给出，所述电压表征在时间段t₂的第一部分期间的信号412： During a first portion of time period _t2 , capacitance switch 410 enables first measurement capacitor 406, and during a second portion of time period _t2 , capacitance switch 410 enables second measurement capacitor 408. The situation during time period _t2 is that _V1 is open. Therefore during the first part of time period _t2 , the voltage

The voltage characterizing the signal 412 during the first part of the time period _t2 is given by the following equation:

[8]，

[8],

where C _R1 represents the resulting capacitance due to C _P1 and C ₁ , which is defined according to the following equation:

[9].

的下述表达，所述电压表征在时间段t₂的第二部分期间的信号412： Similarly, for the case where the second measurement capacitor 408 is enabled, the voltage

The following expression of the voltage characterizing the signal 412 during the second part of the time period _t2 :

[10]。

[10].

Considering equations [8] and [10], it is assumed that the resulting capacity C _R1 remains constant during the time period _t2 . Similar to time period t ₂ , time period t ₁ is associated with a sample frequency of typically 1 kHz to 1 MHz, which is a frequency significantly greater than the bandwidth of first and second fluids 324 and 326 contained in fluid cavity 304 . Therefore, the latter assumption is reasonable and therefore does not degrade the accuracy associated with the measurement of capacitances C ₁ and C ₂ . Combining equations [8] and [10] results in a system of two linear equations containing two unknowns, namely capacitance C ₂ and parasitic capacitance C _p3 . The latter system of linear equations can be solved for the unknown capacitance C ₂ , the solution is given by the following equation:

[11]。

[11].

The measurement circuit 402 also includes a multiplexer 414 that employs time domain multiplexing. The switch circuit 404 cooperates with an input 413 of a multiplexer 414 . A multiplexer 414 replicates a signal 412 representing capacitances _C1 and _C2 into a plurality of signals 416, 418 representing capacitances _C1 and _C2 , respectively. The number of replicates corresponds to the number of auxiliary electrowetting electrodes. After replication, the signals 416 and 418 are demodulated from the demodulated signal through filters 420 and 422, respectively. Filters 420 and 422 are driven by the demodulated signal, which in this particular case is a square wave signal. Consider here a square wave signal, which can reach two values, a low value and a high level. In this particular example, the low value is set equal to zero. The first square wave signal driving filter 420 reaches its high value during time period _t1 , while the second square wave signal driving filter 422 reaches its high value during time period _t2 . Thus, the first square wave signal reaches its high value when voltage _V1 is connected and the second square wave signal reaches its high value when _V2 is connected. As a result, demodulated signals 424 and 426 may be related only to capacitances _C1 and _C2 , respectively.

Note that switching circuit 404 does not have to include a pair of measurement capacitors, that is, a pair of measurement resistors with known resistances that are different from each other or a pair of inductors with known inductances that are different from each other is also feasible. . More generally, linear electronic measuring elements would be feasible. A linear electronic measuring element is defined here as a passive electronic element, ie an electronic element that satisfies a linear relationship between current and voltage, between the time differential of current and voltage or between the time differential of current and voltage. As a result, Equation [4] up to and including Equation [11] will be different.

Referring to Figures 3A and 3B, a voltage control circuit 350 is depicted. The voltage control circuit 350 is arranged for the purpose of controlling the voltages _V1 and _V2 supplied to the auxiliary electrowetting electrodes 318 and 320, respectively, based on the control signal 343 provided by the measurement circuit 342, such that the fluid meniscus 328 The actual geometry is consistent with the desired geometry of the fluid meniscus 328, see Fig. 3A.

表示，其中在此特定实施例的情况下

为二维向量，其包括流体弯月面328分别和壁部308和312之间的每个接触角

₁和

₂的参考。接触角设定点

通过转换表352转换为电容设定点

。在此特定实例中，电容设定点

为二维向量，其包括电容C₁和C₄的参考，即主电润湿电极318和辅助电润湿电极320和322之间的电容。转换表352可以例如通过实验获得。在二维求和点354，电容设定点

与测量电容

比较，其中为包括由测量电路342确定的电容C₁和C₂的二维向量。响应于

和

之间的差异∆，即

，控制器356提供二维电压控制信号358到电压源330。接着，电压源330分别提供前述电压V₁和V₂到辅助电润湿电极320和322。电压控制信号358还被提供到测量电路342，从而使得所述测量电路能够依照方程[7]和[11]进行计算。 For the geometry of the fluid meniscus 328, the desired geometry is determined by the contact angle set point

means, where in the case of this particular example

is a two-dimensional vector that includes each contact angle between fluid meniscus 328 and walls 308 and 312, respectively

₁ and

₂ references. contact angle set point

Convert to capacitive set point via conversion table 352

. In this particular instance, the capacitance set point

is a two-dimensional vector that includes references to capacitances C ₁ and C ₄ , ie, the capacitance between the primary electrowetting electrode 318 and the auxiliary electrowetting electrodes 320 and 322 . The conversion table 352 can be obtained, for example, through experiments. At the two-dimensional summing point 354, the capacitance set point

with measuring capacitance

compare, where is a two-dimensional vector including the capacitances C ₁ and C ₂ determined by the measurement circuit 342 . in response to

and

The difference ∆ between

, the controller 356 provides a two-dimensional voltage control signal 358 to the voltage source 330 . Next, the voltage source 330 provides the aforementioned voltages V ₁ and V ₂ to the auxiliary electrowetting electrodes 320 and 322 , respectively. The voltage control signal 358 is also provided to the measurement circuit 342, enabling said measurement circuit to perform calculations according to equations [7] and [11].

Figure 5 schematically depicts an embodiment of the method according to the invention by means of a flowchart. The method is configured for measuring the geometry of a fluid meniscus between an electrically conductive first fluid and an electrically insulating second fluid contained in a fluid cavity, wherein the fluids are mutually immiscible.

The method includes a step 502 of providing a voltage between a primary electrowetting electrode located in the primary plane and an auxiliary electrowetting electrode located in the auxiliary plane partially surrounding the fluid chamber. , the auxiliary plane is not the main plane. The method also includes step 504: respectively measuring the capacitance between the main electrowetting electrode and at least two auxiliary electrowetting electrodes through a measurement circuit including a multiplexer. The method comprises a step 506 of controlling a voltage provided between said auxiliary electrowetting electrodes based on a signal provided by a measurement circuit.

While the invention has been illustrated and described in detail in the drawings and foregoing description, that illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. For example, the apparatus and method according to the present invention have no limitation on the number of auxiliary electrowetting electrodes, as long as the number is not less than two. Furthermore, the speed of sound of the first fluid and the refractive index of the first fluid may be different from the speed of sound of the second fluid and the refractive index of the second fluid, respectively. In addition, measurements comprising an operational amplifier configured with a negative feedback loop with a measurement capacitance can be employed in conjunction with time-domain multiplexing, wherein the operational amplifier is arranged with the input of the multiplexer terminal collaboration. Note that the device of the invention and all its parts can be manufactured by applying processes and materials known per se. In the claims and the description, the word "comprising" does not exclude other elements, and the indefinite article "a" or "a" does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope. Note also that all possible combinations of features defined in the claims are part of the invention.

Claims (15)

1. An apparatus (102, 302) for measuring the geometry of a fluid meniscus (132, 328), comprising: - a fluid chamber (104, 304) comprising a first fluid (128, 324) and a second fluid (130, 326), the first fluid being electrically conductive, the second fluid being electrically insulating, and the said first and second fluids are mutually immiscible and contact each other at a fluid meniscus (132, 328), - primary electrowetting electrodes (118, 318) and secondary electrowetting electrodes (120, 122, 124, 126) for controlling the geometry of the fluid meniscus, said primary electrowetting electrodes being located in the primary plane (319 ), the auxiliary electrowetting electrodes partially surround the fluid cavity and are located in corresponding auxiliary planes (121, 123, 125, 127), - a voltage source (134, 33) for providing a voltage between said primary electrowetting electrode and a plurality of auxiliary electrowetting electrodes, - a measuring circuit (144, 342) for measuring the capacitance between a primary electrowetting electrode and at least two corresponding auxiliary electrowetting electrodes (320, 322), respectively, said measuring circuit comprising means for demodulating said Multiplexers (212, 414) of signals (210, 412) of respective capacitances. 2. The device according to claim 1, wherein said measuring circuit is arranged for measuring the capacitance between said main electrowetting electrode and each of said auxiliary electrowetting electrodes (120, 122, 124, 12). 3. Apparatus according to claim 1, comprising a voltage control circuit (154, 350) for controlling the voltage across said primary electrowetting electrode and each of said auxiliary electrodes based on a control signal (156, 343) provided by said measurement circuit. The voltage supplied between the electrowetting electrodes. 4. The apparatus according to claim 1, wherein said measurement circuit comprises an operational amplifier (204) for measuring the capacitance between said main electrowetting electrode and at least two of said corresponding auxiliary electrowetting electrodes, wherein said The operational amplifier is configured with a negative feedback loop (206) with a measurement capacitor (208) having a predetermined measurement capacitance, wherein the operational amplifier is arranged for use with the input of the multiplexer (211) Collaboration. 5. The apparatus according to claim 1, wherein said measuring circuit comprises a switching circuit (404) for measuring the capacitance between said main electrowetting electrode and at least two said corresponding auxiliary electrowetting electrodes, wherein said The switching circuit includes a first measuring capacitor (406) having a predetermined first measuring capacitance and a second measuring capacitor (408) having a predetermined second measuring capacitance, wherein the first and second measuring capacitances are different from each other, the switching circuit A capacitive switch (410) for driving the first and second measurement capacitors in an alternating manner is also included, wherein the switch circuit is arranged to cooperate with an input (413) of the multiplexer. 6. The apparatus according to claim 1, wherein said multiplexer is a time domain multiplexer (414), wherein said time domain multiplexer employs demodulated signals, each demodulated signal being A square wave signal having a low value and a high value, wherein said voltage source comprises a voltage switch (331, 333, 407, 409) for alternately disconnecting the voltage corresponding to the high value of the respective demodulated value. 7. The apparatus according to claim 1, wherein said multiplexer is a frequency domain multiplexer (212), wherein said voltage source is arranged to provide a voltage at a specific frequency and wherein said frequency domain multiplexer The multiplexer employs demodulated signals, each demodulated signal having frequency components corresponding to respective specific frequencies. 8. The apparatus of claim 1, wherein the first fluid has a first refractive index and the second fluid has a second refractive index, wherein the first and second refractive indices are different from each other. 9. The apparatus of claim 1, wherein the first fluid provides a first speed of sound and the second fluid provides a second speed of sound, wherein the first and second speeds of sound are different from each other. 10. A catheter (140) comprising the device according to claim 1. 11. Use of the device according to claim 1 in a catheter for ultrasound applications. 12. Use of the device according to claim 1 in an optical storage drive. 13. Use of the device according to claim 1 in an optical camera. 14. A fluid meniscus (132, 328) A method for the geometry of said fluids being mutually immiscible, the method comprising the following steps (502, 504): - providing a voltage between the main electrowetting electrode (118, 318) and the auxiliary electrowetting electrode (120, 122, 124, 126), said main electrowetting electrode being located in the main plane (119, 319), so said auxiliary electrowetting electrode partially surrounds said fluid cavity and is located in auxiliary planes (121, 123, 125, 127), and - by means of a measurement circuit (144, 342) comprising a multiplexer (212, 414), respectively measuring the capacitance. 15. The method according to claim 14, comprising the step (506) of controlling a voltage supplied to said auxiliary electrowetting electrode based on a signal provided by said measurement circuit.

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